Every year, the village of Frei-Weinheim and its inhabitants were exposed to the danger of floods and ice runs. The first reports of these events date back to the 15th century. At that time, dams and locks already existed, but a closed dam system was lacking. The most severe documented natural disaster occurred on February 28, 1784. At that time, the flood carried heavy ice floes that damaged three-quarters of the houses, uprooted trees, and wiped out half of the livestock. As a result, a new dam was constructed by 1795, which had to be renewed again in 1803. The property rights were a recurring issue. Under the Grand Duchy of Hesse government, all land in the dam area was declared state property. This made it possible to create a high and closed dam system along the waterfront in 1825. In the residence of the then-mayor Nikolaus Thorn (Dammstraße No. 3), there was a room for the dam watch at the end of the 19th century. At that time, the diverted Selz flowed beyond the dam, with its mouth forming part of the harbor.
